A polyphenylene ether (PPE) resin is a thermoplastic resin having excellent properties such as mechanical properties, heat resistance, cold resistance, and dimensional stability. However, the polyphenylene ether resin alone shows very poor impact resistance and solvent resistance and also have poor processability because of high melt viscosity thereof. On the other hand, polyamide resins and saturated polyester resins are thermoplastic resins that are excellent in mechanical strength, solvent resistance, and processability, but they are insufficient in impact resistance and heat resistance and also have extremely poor dimensional stability due to high water absorption thereof. In order to take advantage of the desirable properties of the polyphenylene ether resin and the polyamide or saturated polyester resin and to cover the defects of these resins, it has been proposed to blend the both resins. However, since simple blending alone impairs the good mechanical properties possessed by the both resins, use of various compatibilizers at the time of blending the polyphenylene ether resin with the polyamide resin or saturated polyester resin is being practiced so as to improve dispersibility, thereby to attain improved mechanical properties. Such techniques are disclosed, for example, in JP-B-60-11966, JP-B-61-10494, JP-A-59-66452, and JP-A-56-49753. (The terms "JP-B" and "JP-A" as used herein mean an "examined Japanese patent publication" and an "unexamined published Japanese patent application", respectively.) The thus-obtained PPE/polyamide resin or saturated polyester resin compositions are coming to be used as materials having excellent mechanical properties, heat resistance, solvent resistance, processability, dimensional stability, and hygroscopicity, for applications in the fields of electrical-electronic appliances, automotive parts such as external automotive plates, parts located around engine, and wheel covers, etc.
Among such uses, external automotive plates in particular are an application in which coating is requisite.
In a conventional coating method, a shaped part obtained by shaping the above-described material is pretreated with isopropyl alcohol, etc., subsequently a medium called as a primer is applied on the pretreated surface, and then a coating is applied. Such a coating method has a problem that it necessitates a long coating line, causing the cost of a final product to be high. The high cost of a final product is also attributable to expensiveness of the primer itself. Hence, improvements are desired.
Other surface treatments for coating which have been proposed to date include sandblasting, treatment with a chromic acid mixture, flame treatment, corona discharge treatment, plasma treatment, and the like, but satisfactory results have not been obtained with any of these conventional treatments. Because of such circumstances, to develop a new treating method has come to be an important technical theme.